1. Field of the Invention
The present invention relates to a method and an arrangement for membrane filtration of milk in connection with milking.
2. Description of the Related Art
When cows are milked by means of milking machines the flow varies very strongly. The variation is caused partly by the construction of the milking plant and partly by the physiological properties of the cows.
Milking plants work with vacuum and the milk is transported through a pipe line system, which has a vacuum which is fairly equal, to a container usually called an end unit. From this container the milk is pumped, under atmospheric pressure, through a pipe line to a cooling tank or some other storage vessel.
When milk is membrane filtrated in connection to the milking, a membrane filter is connected to the milking plant by way of a balance tank. From this the milk is pumped to a circulation path comprising the membrane filter, in which the milk is divided into two fractions, a concentrate and a permeate. Depending on the choice of filter media these fractions have a different composition. If the milk is to be concentrated by way of ultrafiltration, the permeate consists of water, milk sugar and low molecular salts. If the concentration takes place by way of reverse osmosis the permeate consists of water obtained from the milk.
The membrane filtration usually takes place in direct connection to the milking. After the milking the milk has a temperature of about 35.degree. C. and considering the shelf life it is important that the time the milk is kept at this temperature is kept as short as possible.
The milk is transported from the end unit by way of a milk filter, in which coarser contaminations are separated off, to the balance tank and is from there pumped to the circulation path of the membrane filter.
When the level in the balance tank has fallen to a certain predetermined value, the pump which transports the milk to the circulation path stops. At this time there are consequently residues of milk in the end unit, in the pipe lines between this unit and the balance tank and in this tank.
The milking plant as well as the components which are included in the membrane filtration equipment must be cleaned after each milking. The milk which is left in the plant will if no measures are taken be lost during the washing and consequently represents a loss to the milk producer.